re: attacking an object...What I'm reading suggests to me that... if you choose to make an attack roll, you get an automatic Crit if you hit what you're attacking. At the same time... it doesn't indicate what happens if you miss. I'm sort of leaning towards a miss result means you actually miss -or at least fail to hit the object in a meaningful way.

The Forcefield has an active defense of Zero (0), and is Huge (-2), so it can be hit on a result of 8 or better. Spartan's 5 ain't going to cut it. Before I adjudicate the forcefield damage, I'd like some input as to whether that's correct or appropriate.

That's kind of the way I always interpreted it. You don't have to make an attack roll for most stationery objects it'd be just making a routine check but if you do make the check and hit it's a finishing attack (crit). If you make the attack and don't hit then I'd say you either miss or if it makes no sense to miss (it's a huge fricken field) do no harm.

Yeah, a miss I'd either rule that the attack missed the target or hit the target but as a glancing blow or somesuch (no damage). I purposely rolled because I'd prefer to take the force field out in one or two turns if at all possible.